The present invention relates to the field of adjustable chairs and, in particular, to an office chair having an adjustable backrest.
The typical office chair consists of a seat portion and a backrest portion and, optionally, armrest portions, all supported by a pedestal, usually having wheels thereon for movement of the chair about the work area. It is well known in the prior art for the backrest portion of the chair to be adjustable from an upright position to a position that is semi-reclined, usually as the result of pushing back of the backrest by a person seated in the chair. The seat portion of the chair may or may not move in accordance with the backrest portion when it is reclined. Typically, the backrest portion is coupled with a spring such that when pressure is released on the reclining backrest portion, the backrest portion returns to an upright position.
In many instances, it may be desirable to limit the motion of the backrest portion of the chair. The limiting of the motion of the backrest can be in one of two forms. First, the distance that the backrest can be reclined can be limited and, second, when the backrest is reclined, the backrest can be prevented from returning to the upright position when pressure is released, thereby leaving the chair in a reclined position.
One simple way to accomplish the locking of the backrest in various configurations is to have one or more locking members which can be inserted into recesses in the chair frame at the appropriate places to limit the movement of the backrest. However, one problem with this mechanism is that movement of the locking members into and out of the recesses tends to bind when pressure is being applied to the backrest, either by the backwards pushing of a person sitting in the chair or by the movement of the backrest to the upright position as a result of springs in the chair. As a result of the binding, the locking members will be unable to move into and out of the recesses.
In the type of movement limiting device described, the locking member is typically adjusted by the user through the use of a lever attached to the side of the chair, which is easily accessible to a person sitting in the chair. The lever may be attached to a cable which is in turn attached to the mechanism for moving the locking members into and out of the recesses in the frame of the chair. One problem with this mechanism is that it may be desirable to have one stop on each side of the chair frame, to ensure even operation. Therefore, a mechanism is needed to translate the motion of a single cable into a back and forth motion capable of moving one or more locking members. The second problem with such a mechanism is that when the locking members are bound by pressure applied by the backrest of the chair, the locking members will not move when the person seated in the chair actuates the cable. If the user exerts enough pressure on the bound mechanism, it can result in the breaking of any one of a number of parts in the linkage from the lever to the locking members. Therefore, it would be desirable to have a device which, first, translates the movement of a lever-actuated cable into a back and forth motion that can slide the locking members into and out of the recesses and, second, allows movement of the cable in response to the user actuating the lever connected to the cable without damaging the translation mechanism.
The present invention provides a mechanism using a rack and pinion gear configuration that is capable of translating the motion of a cable to the back and forth motion of one or more locking members with respect to one or more corresponding recesses in the chair frame. The mechanism also incorporates an overload protection device whereby movement of the cable, when the locking members are bound in the recesses, results in compression of springs which store the energy necessary to move the locking members with respect to the recesses once the binding is removed.
The mechanism is constructed generally of a housing and a member able to slide radially within the housing. A spring is disposed between the slide member and the housing which is compressed when the slide member slides within the housing, but when the housing is unable to move due to a binding condition. The slide member is attached to a cable which, when tensioned, causes motion of the slide member within the housing such as to compress the spring, thereby urging the housing in a first direction. An additional spring is disposed between the end of the cable and the housing to urge the housing in the opposite direction when the tension on the cable is released. Attached to the housing with a rack and pinion assembly are two actuators which, when rotated by the rack and pinion assembly, cause one or more locking members to be inserted into or withdrawn from recesses defined in the chair frame. The presence of the locking members in the recesses results in the locking of some aspect of the chair, such as the backrest.